Considerations on the modelling and optimisation of resolution of ionisable compounds in extended pH-range columns

The problems associated to the modelling and optimisation of the chromatographic resolution of mixtures involving ionisable solutes at varying pH and acetonitrile content are discussed. Several retention models that separate the contributions of solute, column and stationary phase, were used. The retention was predicted with low errors in large pH domains (2-12), which was an essential requirement to face the optimisation of resolution. The selected mixture was particularly problematic under the viewpoint of resolution, owing to the excessively diverse acid-base behaviour of solutes. This variety led to sudden drops in retention at different pH for each solute, yielding numerous peak crossing, which made finding shared regions of high resolution especially difficult. Conventional resolution diagrams for these situations are scarcely informative, since both the overall and the worst elementary resolutions drop to zero if at least two compounds remain overlapped, even when all the others are baseline resolved. A new chromatographic objective function is proposed to address this drawback. This function, called "limiting peak count", is based on the limiting peak purity concept, and measures the success in the resolution focusing on the resolved solutes, in contrast to conventional resolution assessments that attend mainly to the least resolved solutes. Limiting peak count yields the same result as conventional assessments when full resolution is possible, but it is also able to discriminate the maximal resolving power in low-resolution situations. It offers a different perspective to that given by the complementary mobile phases approach, and the computation is far simpler.     

Structure of the liquid-vapor interface of water-methanol mixtures as seen from Monte Carlo simulations

Monte Carlo simulation of the vapor-liquid interface of water-methanol mixtures of different compositions, ranging from pure water to pure methanol, have been performed on the canonical (N, V, T) ensemble at 298 K. The analysis of the systems simulated has revealed that the interface is characterized by a double layer structure: methanol is strongly adsorbed at the vapor side of the interface, whereas this adsorption layer is followed at its liquid side by a depletion layer of methanol of lower concentration than in the bulk liquid phase of the system. The dominant feature of the interface has been found to be the adsorption layer in systems of methanol mole fractions below 0.2, and the depletion layer in systems of methanol mole fractions between 0.25 and 0.5. The orientation of the molecules located at the depletion layer is found to be already uncorrelated with the interface, whereas the methanol molecules of the adsorption layer prefer to align perpendicular to the interface, pointing straight toward the vapor phase by their methyl group. Although both the preference of the molecular plane for a perpendicular alignment with the interface and the preference of the methyl group for pointing straight to the vapor phase are found to be rather weak, the preference of the methyl group for pointing as straight toward the vapor phase as possible within the constraint imposed by the orientation of the molecular plane is found to be fairly strong. One of the two preferred orientations of the interfacial water molecules present in the neat system is found to disappear in the presence of methanol, because methanol molecules aligned in their preferred orientation can replace these water molecules in the hydrogen-bonding pattern of the interface.     

Synthesis of isomeric β-haloethylthienopyrroles

The preparation of ethyl 4-(2-bromoethyl)thieno[2,3-b]pyrrole-5-carboxylate and ethyl 6-(2-bromoethyl)thieno[3,2-b]pyrrole-5-carboxylate by reaction of t-butyl 2-(2-thienyl)carbazate and t-butyl 2-(3-thienyl)carbazate with ethyl-5-bromo-2-oxopentanoate are described.     

Study of the interferences in the determination of Pu, Am and Cm in radioactive waste by extraction chromatography

This paper describes the experimental studies carried out to determine (238)Pu, (239/40)Pu, (241)Pu, (241)Am, (242)Cm and (244)Cm in samples from nuclear power plants (mainly spent ion exchange resins and evaporator concentrates) using an organophosphorus compound immobilized on an inert support. These materials are commercially available under the name TRU Resin (for Transuranium Specific) from Eichrom Industries, Darien, IL. An attempt is made to develop a rapid, accurate method of analysis, with minimum waste generation. Standard solutions of Pu and Am and one sample of spent ion exchange resin that contains fission, activation products, Pu, Am and Cm were analyzed to study the separation factors and interferences in the measurement of Pu, Am and Cm isotopes.     

铜(Ⅱ)-4-(喹啉-8′-甲基)-1,4,7,10-四氮杂环十三烷-11,13-二酮-α-氨基酸或5-取代邻菲罗啉两类三元配合物的稳定性研究

用 p H法在 (2 5.0± 0 .1 )℃ ,I=0 .1 mol· dm-3 KNO3 条件下 ,测定 Cu( ) - 4 - (喹啉 - 8′-甲基 ) - 1 ,4,7,1 0 -四氮杂环十三烷 - 1 1 ,1 3-二酮 -α-氨基酸或 5-取代邻菲罗啉两类三元配合物的稳定常数 ;研究了带甲基喹啉侧基大环多胺配体与 Cu( )离子的配位能力、配位方式 ;发现这两类三元体系配合物有特殊的稳定性 ;而且它们的稳定性与配体α-氨基酸及 5-取代邻菲罗啉酸碱强度之间的直线自由能关系的变化趋势相反 ;探讨了 Cu( )和 5-取代邻菲罗啉之间的 d- p反馈π键及其取代基 Hammett诱导效应的关系。     

Selectivity of Several Liquid Phases for the Separation of Pine Terpenes by Gas Chromatography

Chromatographic retention data and thermodynamic properties of six pine terpenes (α-pinene, β-pinene, camphene, limonene, α-phellandrene and p-cymene) on six different liquid phases, with a wide range of polarity, are reported at temperatures from 80 to 120 °C. The retention behaviour and selectivity of liquid phases for the separation of binary solute systems are discussed in terms of activity coefficients and specific interactions. Solubility parameters for the liquid phases are reported using the regular solution theory and the Takamiya equation and a good correlation between polarity and solubility parameters is observed.     

Combining thermal analysis with other techniques to monitor the decomposition of poly(m-phenylene isophthalamide)

The pyrolysis behaviour of Nomex, poly(m-phenylene isophthalamide) fibres under argon has been investigated up to a temperature of 1173 K with different methods to get direct information on the progressive changes taking place in the solid material and its carbon fibre residues. The main stages of the pyrolytic degradation of the fibres were determined by thermal analysis (TG and DTA) and their chemical and morphological evolution through the different steps was subsequently followed by Fourier transform infrared spectroscopy (FTIR) and atomic force microscopy (AFM) measurements, respectively, on samples treated to various temperatures. This revised version was published online in July 2006 with corrections to the Cover Date.     

3－苯氧甲基－6－（2，4－二氟苯基）－7H-1,2,4-三唑并[3,4-b][1,3,4]噻二嗪的合成与晶体结构研究

由苯氧乙酸出发，经多步反应，制得3-苯氧甲基－4－氨基－5－巯基－1，2， 4－三唑，它与2-氯－2'，4'－二氟苯乙酮进行环化反应，生成3-苯氧甲基－6－（ 2,4-二氟苯基）－7H-1,2,4-三唑并[3,4-b][1,3,4]噻二嗪，通过元素分析、红外 光谱、核磁共振氢谱与碳谱、质谱进行表征，并利用单晶X射线衍射法测定其结构 。晶体属单斜晶系、P2_(1/c)空间群，a = 1.339(3) nm, b = 1.4683(4) nm, c = 0.8606(2) nm, β = 108.49(2)°, Z = 4, F(000) = 736, R_1 = 0.0509。还 对均三唑并噻二唑两类稠杂环的晶体结构作了比较。     

Liquid chromatography of carbon clusters

Summary A comparison of three binary mobile phases in LC separation of C₆₀ and C₇₀ fullerences on chemically bonded 2,4-dinitroanilinopropyl (DNAP) stationary phase was carried out, n-Hexane-benzene has been found to be the best mobile phase for efficient separation of the all-carbon molecules permitting high loads in preparative LC.     

Thermal studies on metal complexes of 5-nitroso-pyrimidine derivatives

The following cadmium(II) complexes of deprotonated 6-amino-5-nitroso-uracil (AH), deprotonated 6-amino-3-methyl-5-nitroso-uracil (BH) and neutral 6-amino-1-methyl-5--nitroso-uracil (CH) have been prepared and their thermal behaviour studied by TG and DSC techniques: CdA₂ · 3 H₂O, CdB₂ · 2 H₂O, CdB₂ and CdCl₂(CH)₂ · 2 H₂O.Dehydration processes of these complexes take place in only one step and the enthalpy values associated with them are comprised in the 42.7–80.5 kJ · mole^–1 H₂O range. The pyrolytic reactions finish in the 630–900 C temperature range, remaining as final residue in the case of CdA₂ · 3 H₂O, CdB₂ · 2 H₂O and CdB₂ complexes, cadmium oxide. The pyrolytic decomposition of CdCl₂(CH)₂ · 2 H₂O complex does not yield any residue, due to the elimination of cadmium chloride.

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Zusammenfassung Folgende Cadmium(II)-Komplexe von deprotoniertem 6-Amino-5-nitrosouracil (AH), deprotoniertem 6-Amino-3-methyl-5-nitroso-uracil (BH) und neutralem 6-Amino-1-methyl-5-nitroso-uracil (CH) wurden hergestellt: CdA₂ · 3 H₂O, CdB₂· 2 H₂O, CdB₂ und CdCl₂(CH)₂ · 2 H₂O. Das thermische Verhalten dieser Komplexe wurde mittels TG und DSC untersucht. Die Dehydratisierung der Komplexe verlÄuft in nur einem Schritt. Die Enthalpiewerte für diese Prozesse liegen im Bereich von 42.7–80.5 kJ · mol^–1 H₂O. Die pyrolytischen Reaktionen verlaufen im Temperaturbereich von 630–900C zu Ende, wobei im Falle der Komplexe CdA₂ · 3 H₂O, CdB₂ · 2 H₂O und CdB₂ Cadmiumoxid als Rückstand zurückbleibt. Die pyroytische Zersetzung von CdCl₂(CH)₂ · 2 H₂O verlÄuft wegen der Flüchtigkeit von CdCl₂ rückstandslos.

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CdA₂ · 3 H₂O, CdB₂ · 2 H₂O, CdB₂ CdCl₂(CH)₂ · 2 H₂O, A — 6--5-, B — 6--3--5- CH — 6--1--5- . . 42.7–80.5 · ^–1. 630–900, . CdCl₂(CH)₂ · 2 H₂O - , .